To chime in with my opinion on the THU rig player and rig libraries. I have found the rig libraries to be immediately and noticeably much better then any non rig sounds included in TH2, 3 or U. I am currently replacing all guitar sounds in my earlier recording projects that were using Guitar Rig 5, Amplitube Max, and of course, TH2, 3, and U tweaked standard presets (non rig) with sounds from the THU rig libraries. Admittedly I have not tried to tweak the sounds in the rig libraries but then again I find that there are so many preset sounds that are superior and are far more authentic I do not feel the need to do so. I do have a friend that owns a Kemper and both he and I think it is an incredible piece of gear.
The THU rig lib sounds so much more realistic to me that I think they do rival the Kemper in terms of producing fantastically realistic sounding examples of the amplifiers and cabinet combinations they are modeling. I believe it is the single greatest improvement I have heard in a guitar modeling plug-in to date in terms of authenticity of sound for in the box recording. I own full versions of Guitar Rig 5 and Amplitube Max. Neither come anywhere near the rig models for THU. Clearly my new go to plug in for guitars.
~Try one and see for yourself. I think you will really like them.